The biotechnological process of producing ethanol in alcohol distilleries is done such that a mash of hydrolyzed, carbohydrate-containing material is fermented and subsequently completely freed of alcohol in a mash column by heating it directly with steam, and the escaping water-alcohol mixture is fed into a rectifying column. A residual solution is discharged from the mash column, which presents an environmental problem. According to a DECHEMA study on research and development in the field of biotechnology, pp. 121-122, which was done in 1974 by order of the Federal Ministry for Research and Technology in Germany, approximately 2 million m.sup.3 of residue from starchy raw materials accumulate each year in the Federal Republic. This residue contains 25 000 mg O.sub.2 /l, which represents a very high BSB.sub.5 value (biochemical oxygen requirement for a 5-day period). The residual materials cannot be stored and can only be used directly as feed. It would be desirable to have the product dried in order to use it as feed admixture. According to K. R. Dietrich (see H. Kretzschmar, "Yeast and Alcohol," Springer publication, Berlin, Gottingen Heidelberg, pp. 506 to 509, 1955), the residue, which is discharged at the bottom of the mash column, can be led over a strainer, the resulting solid materials can be pressed, the accumulating fluid can be boiled down in a multi-evaporator and the concentrated mass can subsequently be dried with the aid of drum dryers. According to the above mentioned DECHEMA study, such a drying process is not economical in the Federal Republic for energy-political reasons and in view of the size of such operations.